From: Rik van Riel <riel@redhat.com>
To: Nitin Gupta <nitingupta.mail@gmail.com>
Cc: linux-mm@kvack.org
Subject: Re: a basic question
Date: Sat, 22 Oct 2005 14:11:33 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.63.0510221409460.6999@cuia.boston.redhat.com> (raw)
In-Reply-To: <f68e01850510220909wad86b06wadc620fb5f807b5d@mail.gmail.com>
On Sat, 22 Oct 2005, Nitin Gupta wrote:
> - How does processor know that 3GB-4GB is mapped linearly on first 1GB
> of memory. Is there a pagetable for this segment mapping it linearly?
Yes, there are page tables for this.
> - Why isn't it like this - userspace tasks have 4GB virtual address
> space and for kernel also a 4GB virtual address space that is linearly
> mapped to fist 4GB of memory.
With the 4:4 split patch, this is done. However, there is a
cost to this approach - every time the system switches from
user mode to kernel mode it goes through a context switch.
An extra two context swiches on every system call, every
interrupt. For most systems the gained space is simply not
worth the time overhead.
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prev parent reply other threads:[~2005-10-22 18:11 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-22 16:09 Nitin Gupta
2005-10-22 18:11 ` Rik van Riel [this message]
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